Recently, a diversity of document processing machines such as printers, facsimile machines, multifunction peripherals, scanners or automatic document feeders (ADFs) are widely used to process documents such as paper sheets. A document processing machine often has a document-feeding device for successively feeding a stack of documents into the inner portion of the document processing machine so as to implement associated operations such as scanning, faxing, scanning operations and the like. Generally, the document-feeding device has a sheet-separating structure for separating the top paper sheet from the stack of paper sheets, thereby picking a single paper sheet. As a result, the paper sheets may be transported into the document processing machine one by one.
Referring to FIG. 1, a schematic partial cross-sectional view of a conventional document-feeding device is illustrated. The document-feeding device 1 principally includes a sheet-feeding channel 11 and a sheet-separating structure 12. The sheet-feeding channel 11 is used to support the paper sheets. The sheet-separating structure 12 is disposed within the sheet-feeding channel 11, and includes a separation roller 121, a separation pad 122, a base 123 and an elastic element 124. The rotation of the separation roller 121 may facilitate transport of the paper sheet. The base 123 is received in a recess structure 111 within the sheet-feeding channel 11 for supporting the separation pad 122. The separation pad 122 is attached on the surface of the base 123. The elastic element 124 is disposed in the recess structure 111 for supporting the base 123 such that the separation roller 121 is always sustained against the separation pad 122.
The operation principle of the sheet-separating structure 12 will be illustrated as follows with reference to FIG. 1. When the frictional force between the paper sheet and the separation roller 121 is greater than the frictional force between the paper sheets or greater than the paper sheet and the separation pad 122, the uppermost paper sheet (i.e. the closest paper sheet to the separation roller 121) is nipped between the separation roller 121 and the separation pad 122. By cooperation of the separation roller 121 and the separation pad 122, the uppermost paper sheet will be separated from the stack of paper sheets so that only one paper sheet is picked to implement associated operations such as scanning, faxing, scanning operations and the like.
The sheet-separating structure 12 of the document-feeding device 1, however, still has some drawbacks. For example, it is difficult to elaborately control transfer of the paper sheet by means of only the separation roller 121, which is arranged on one side of the paper sheet. In addition, although the separation pad 122 is in contact with the paper sheet for offering a frictional force, the separation pad 122 lacks the function of directly driving movement of the paper sheet. Under this circumstance, the separation pad 122 is readily abraded and the operating life thereof is often reduced.